Secondary metabolites of an Algerian Phlomis bovei and their antioxidant activities

Abstract

The plants of the genus Phlomis are native to Turkey, North Africa, Europe, and Asia. Phlomis bovei De Noe, syn. Phlomis samia Desfontaines (Lamiaceae), is a rare Algerian endemic plant, commonly known as Kayat El Adjarah [1] in the Algerian dialect or variously named Farseouan, Tarseouan, Iniji, R ilef, and Azaref throughout the North of Africa [2]. It is one among the nine endemic plants recorded in the Rapport National sur la Diversite Biologique [1]. P. bovei is a herbaceous perennial plant, which grows up to 0.8 m and often develops a stout woody base. Phlomis bovei was collected from the east of Algeria in june 2006 and was taxonomically identified by Dr. Hocine Laouer from the Department of Biology, University of Setif. About 465 g of the air powdered leaves were extracted with n-hexane, CH2Cl2, and MeOH in succession at room temperature. The MeOH extract was fractionated over silica gel–VLC eluting with CH2Cl2 followed by increasing concentrations of MeOH. Fractions 3 and 4 (41 g), eluted with CH2Cl2–MeOH 50:50–25:75), were combined and further applied to column chromatography over silica gel using CH2Cl2–EtOAc and EtOAc–MeOH. Fraction L (1.73 g), eluted with 95:5 EtOAc–MeOH, was subjected to RP18 MPLC with H2O–MeOH. Purification of fraction L6 (18 mg) by Sephadex LH20 (MeOH) allowed the isolation of compound 1. Purification of fraction L17 (112 mg) by SPE RP18 MeOH–H2O and TLC on silica gel (9–1) CH2Cl2–MeOH afforded compound 2. Fraction L22 (62 mg) was subjected to SiO2 TLC using (EtOAc– MeOH–H2O 100:10:5), yielding 3 (9 mg). The structures of these compounds were elucidated by UV, 1H NMR, and 13C NMR, and all these data were in good agreement with the respective literature data [3–8]. Compound 1, C15H10O5, mp 347 C, UV (MeOH, max, nm): 266, 330; +NaOH: 275, 324, 390; +AlCl3: 277, 301, 341, 387; +AlCl3/HCl: 277, 301, 341, 387; +NaOAc: 278, 300, 380; +NaOAc/H3BO3: 273, 279, 350. 1H NMR (400 MHz, CD3OD, , ppm, J/Hz): 7.78 (2H, d, J = 8.9, H-2 , H-6 ), 6.90 (2H, d, J = 8.9, H-3 , H-5 ), 6.51 (1H, s, H-3), 6.42 (1H, d, J = 2.1, H-8), 6.22 (1H, d, J = 2.1, H-6). This compound was characterized as 5,7,4 -trihydroxyflavone (apigenin) [6]. Compound 2, C21H20O10, mp 226–228 C, MS–ES positive 433, UV (MeOH, max, nm): 269, 334; + NaOH: 267, 381; + AlCl3: 277, 349 sh, 383; + AlCl3/HCl: 279, 346 sh, 382. 1H NMR (400 MHz, CD3OD, , ppm, J/Hz): 7.91 (2H, d, J = 8.8, H-2 , H-6 ); 6.95 (2H, d, J = 8.8, H-3 , H-5 ); 6.83 (1H, d, J = 2.5, H-8); 6.51 (1H, s, H-3), 6.54 (1H, d, J = 2.55, H-6); 5.20 (1H, d, J = 7.5, H-1 Glu); 3.05–3.90 (sugar protons). Identified as apigenin 7-O-glucoside or apigetrin [7]. Acid hydrolysis of 2 produced apigenin and D-glucose. Compound 3, C10H10O2, mp 110 C, 1H NMR (400 MHz, CD3OD, , ppm, J/Hz): 7.66 (2H, d, J = 8.85, H-2 , H-6 ); 6.73 (2H, d, J = 7.56, H-3 , H-5 ); 6.85 (1H, d, J = 12.6, H-4); 5.72 (1H, d, J = 12.6, H-3), 13C NMR (CD3OD, 75 MHz): 112.6 (C-3), 116.7 (C-3 ,5 ), 126.6 (C-1 ), 133.9 (C-2 ,6 ), 145.6 (C-4), 170 (C-2). Identified as 4-(4 -hydroxyphenyl)-trans-but-3en-2-one [8].